The present invention relates to electromechanical programmer/timers for use in controlling the program functions of an electrically operated appliance. Timers of this type are commonly employed for sequentially controlling the functions of clothes washing machines, dish washers and clothes driers during a user-selected program interval. Typically, the appliance user rotates a selector knob, having a pointer, to a desired dial position for selecting the length of the appliance operating program interval.
In appliance programmer timers, employing a cam drum rotatable for sequentially actuating a plurality of electrical switches for controlling the appliance functions during the program, one of the more widely used techniques for advancing the cam drum is that of oscillating an advance pawl contacting peripheral ratchet teeth provided on the cam drum. Typically, in ratchet and pawl cam advance mechanisms, the leading edge of the ratchet teeth has a greater slant than the trailing edge to permit the pawl to ramp over the tooth on the pawl return stroke and drive against the trailing edge of the tooth on the forward stroke for advancing the ratchet. Such an arrangement thus renders the cam drum capable of user rotation in a forward direction only where the pawl can be "dragged" or ramped over the ratchet teeth during user rotation for initially positioning the cam drum and selection of the desired program interval. However, reverse rotation of the cam drum by the user for program interval selection is precluded by the pawl point being wedged into the base of the ratchet teeth by virtue of the generally radial or reverse incline slope of the trailing edge of the ratchet teeth.
This arrangement of pawl and ratchet advanced appliance programmer/timer cam drums has been found to be somewhat inconvenient for user Program interval selection because the dial must often be rotated nearly a full revolution in order to obtain the desired program interval setting. Thus, it has been desired to find a way or means of enabling bi-directional rotation of the user selection knob employed on an electromechanical appliance programmer/timer having a pawl and ratchet advanced cam drum.